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[kernel] Update syscall MSRs for all CPUs

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Since SYSCALL/SYSRET rely on MSRs to control their function, split out
syscall_enable() into syscall_initialize() and syscall_enable(), the
latter being called on all CPUs. This affects not just syscalls but also
the kernel_to_user_trampoline.

Additionally, do away with the max syscalls, and just make a single page
of syscall pointers and name pointers. Max syscalls was fragile and
needed to be kept in sync in multiple places.
This commit is contained in:
Justin C. Miller
2021-02-10 01:15:32 -08:00
parent 70d6094f46
commit 872f178d94
5 changed files with 64 additions and 47 deletions
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67
src/kernel/syscall.s
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@@ -1,17 +1,32 @@
%include "tasking.inc"
; Make sure to keep MAX_SYSCALLS in sync with
; syscall::MAX in syscall.h
MAX_SYSCALLS equ 0x40
; SYSCALL/SYSRET control MSRs
MSR_STAR equ 0xc0000081
MSR_LSTAR equ 0xc0000082
MSR_FMASK equ 0xc0000084
; IA32_STAR - high 32 bits contain k+u CS
; Kernel CS: GDT[1] ring 0 bits[47:32]
; User CS: GDT[3] ring 3 bits[63:48]
STAR_HIGH equ \
(((1 << 3) | 0)) | \
(((3 << 3) | 3) << 16)
; IA32_FMASK - Mask off interrupts in syscalls
FMASK_VAL equ 0x200
extern __counter_syscall_enter
extern __counter_syscall_sysret
extern syscall_registry
extern syscall_invalid
global syscall_handler_prelude
global syscall_handler_prelude:function (syscall_handler_prelude.end - syscall_handler_prelude)
syscall_handler_prelude:
push rbp ; Never executed, fake function prelude
mov rbp, rsp ; to calm down gdb
.real:
swapgs
mov [gs:CPU_DATA.rsp3], rsp
mov rsp, [gs:CPU_DATA.rsp0]
@@ -36,14 +51,7 @@ syscall_handler_prelude:
inc qword [rel __counter_syscall_enter]
cmp rax, MAX_SYSCALLS
jle .ok_syscall
.bad_syscall:
mov rdi, rax
call syscall_invalid
.ok_syscall:
and rax, 0xff ; Only 256 possible syscall values
lea r11, [rel syscall_registry]
mov r11, [r11 + rax * 8]
cmp r11, 0
@@ -52,8 +60,14 @@ syscall_handler_prelude:
call r11
inc qword [rel __counter_syscall_sysret]
jmp kernel_to_user_trampoline
global kernel_to_user_trampoline
.bad_syscall:
mov rdi, rax
call syscall_invalid
.end:
global kernel_to_user_trampoline:function (kernel_to_user_trampoline.end - kernel_to_user_trampoline)
kernel_to_user_trampoline:
pop r15
pop r14
@@ -70,3 +84,28 @@ kernel_to_user_trampoline:
swapgs
o64 sysret
.end:
global syscall_enable:function (syscall_enable.end - syscall_enable)
syscall_enable:
push rbp
mov rbp, rsp
mov rcx, MSR_STAR
mov rax, 0
mov rdx, STAR_HIGH
wrmsr
mov rcx, MSR_LSTAR
mov rax, syscall_handler_prelude.real
mov rdx, rax
shr rdx, 32
wrmsr
mov rcx, MSR_FMASK
mov rax, FMASK_VAL
wrmsr
pop rbp
ret
.end: